Process for obtaining indium and tin from raw lead



United States Patent 3,462,352 PROCESS FOR OBTAINING INDIUM AND TIN FROM RAW LEAD Tudor Segarceanu, str. Ciurea 7, Andrei Cornea, strada Aleea Tibles 56, and Viorica Mercea, strada Elena Clucereasa 46, all of Bucharest, Rumania N0 Drawing. Filed Feb. 27, 1967, Ser. No. 619,065

Int. Cl. C22d N20 US. Cl. 204-105 4 Claims ABSTRACT OF THE DISCLOSURE A process for separating indium and tin from impure lead containing them which comprises the steps of concentrating the electrolyte solution used for the electrolytic refining of raw lead in fiuosilicic acid medium by recycling the solution to obtain a minimum ratio of lead to tin of 10, liquid-liquid extracting the electrolytic solution with a solution of di(2-ethyl-hexyl) phosphoric acid in kerosene at room temperature, separating the phases, thereafter washing the organic phase with fiuosilicic acid to remove lead, re-extracting the indium from the organic phase with 9 N HCl, r e-extracting the tin with 8 N HCl, recycling the organic phase for extraction, recycling the aqueous phase as an electrolyte, and recovering indium and tin.

The present invention relates to a process for the quantitative recovery of indium and tin from raw lead containing them, as well as to the further separation of these components present as impurities in the raw lead.

It is known to carry out a pyrometallurgic process for the recovery of indium and tin by the alkaline oxidative refining of the raw lead, whereby the major portion of indium and tin are collected in the indium crusts. These crusts are then further treated by chemical methods for separating indium and tin. The disadvantages of this process are that a low recovery of indium and tin results therefrom and the technology is complicated.

It is also known to carry out an electrolytic process consisting of the concentration of indium and of a fraction of the tin contained in the electrolyte used for the electrolytic refining of the raw lead. Although in the case of the electrolytic process, higher indium recovery is obtained as compared to recovery in the pyrometallurgic process, the disadvantages of the electrolytic process are much the same as in the case of the pyrometallurgic process. Thus, by the known electrolytic process, there can be obtained only a maximum recovery of 7075% of the original indium. Since in the electrolytic process, indium is distributed in two different and distinct by-product fractions, i.e. about 60-70% of the total in the anodic mud and about 3040% in the soluble state in the electrolyte, there are therefore necessary for recovery, two distinct and different separation technologies both requiring a high reagent consumption. Furthermore, the recovery of tin under normal conditions is achieved to the extent of 10- the rest remaining in the electrolytic lead. In the event there is higher tin recovery, higher losses of lead also result because the lead remaining in the electrolyte is transformed into lead sulfate. In the extraction of indium from the electrolyte, the entire amount of fiuosilicic acid is transformed into sodium fiuosilicate and thus the electrolyte cannot be further recycled to the electrolysis. This disadvantage added to the others leads to economic disadvantages for the recovered products.

The process of this invention eliminates the above mentioned disadvantages. To carry out the invention, in the first step, the indium and tin contained in the raw lead ice are concentrated in the electrolyte obtained from an aqueous solution of 1l6130 g. fiuosilicic acid/l. previously used for the electrolytic refining of the raw lead. This is accomplished by maintaining the electrolyte in recycle to the electrolysis bath until a suitable tin concentration is attained; that is, when the PbzSn ratio in the electrolyte is reduced to a minimum value of 10. Then in a second step, the tin and indium contained in the electrolyte are separated by liquid-liquid extraction with a solution containing 0.81.2 mole of di-Z-(ethyl-hexylic) phosphoric acid in refined kerosine, the contact time of the two solutions being about 30-60 minutes and the ratio of aqueous phase to organic phase being 0.67-3 at a normal temperature. The organic phase in which tin and indium were extracted from the electrolyte is washed, after decantation from the aqueous phase with an aqueous solution of fiuosilicic acid to separate the lead extracted at the same time with tin and indium. Then the re-extraction of indium from the organic phase is carried out with a solution of 9 N HCl, the contact time being about 8-10 minutes and the re-extraction of tin is subsequently carried out with a solution of 8 N HCl, the contact time being about 5565 minutes. The organic phase as well as the electrolyte (aqueous phase) is suitable for recycling. The indium and tin in the aqueous phases obtained from the re-extractions are subsequently treated by known methods by cementation on aluminum sheet, at a pH of 12 and by melting under sodium hydroxide to yield the pure elements.

Three examples of the application of the process according to the invention are presented hereinbelow although these examples are intended only as embodiments of the invention and it is in no way intended to limit the invention thereto.

Example 1 Ten kg. of raw lead containing 0.8% of indium and 0.6% of tin are submitted to electrolytic refining under the following conditions: the electrolyte is composed of 130 g. fiuosilicic acid/l. and -90 g. lead/1.; the current density is of a./m. At the end of the electrolytic refining operation, 9.8 kg. of lead having a purity of 99.95% are obtained, which contains in addition 0.01% of tin and 0.003% of indium. There are also obtained 10 liters of electrolyte containing 7.9 g. of indium and 5.8 g. of tin per liter of electrolyte.

For the separation of indium and tin, the resulting electrolyte is mixed with a solution of 1 molar di-(2- ethylhexyl) phosphoric acid in kerosine. Mixing is achieved by stirring for 40 minutes; the ratio of aqueous phase to organic phase being equal to 1.25. There are thus obtained 8 liters of an organic phase containing 9.75 g. indium/l. and 6.15 g. tin/l. This organic phase into which indium, tin, and a part of the lead were extracted, is washed with a solution of 200250 g. fiuosilicic acid/l. A ratio of organic phase to aqueous phase of 12:1 is used in order to eliminate the extracted lead. After this washing operation, there is obtained 0.7 l. of an aqueous solution containing 77 g. lead/1., 1 g. indium/1., 0.38 g. tin/1., and 200 g. fiuosilicic acid/1. This aqueous solution is added to the electrolyte whose indium and tin were extracted, and is recycled into the new electrolysis step.

For the re-extraction of indium, the organic phase is then treated with a solution of 9 N HCl, the ratio organic phase to aqueous phase being 20:1 and the contact time being about 8-10 minutes. 0.4 liters of an aqueous solution containing 193 g. of indium per liter are obtained. Subsequently, the organic phase is treated for the reextraction of tin with a solution of 8 N HCl, the ratio of organic phase to aqueous phase being 14:1, and the contact time being about 60 minutes. There are obtained 0.53 l. of a solution containing 81.5 g. tin/l.

Example 2 Raw lead containing the same amounts of indium and tin impurities as in Example 1 is electrolyzed, but the electrolysis is operated to give a high concentration of indium in the electrolyte.

37 kilograms of raw lead are subjected to electrolysis under the same operating conditions (the electrolyte composition, the current density, etc.) as in Example 1. There are obtained 36.3 kg. of lead, containing O.46-0.5% of tin. There remains in the resulting electrolytic lead product 76% of the original tin. There are also obtained liters of electrolyte containing 29 g. indium/1., 39 g. lead/1., and 4 g. tin/l.

In order to extract the indium and tin, the electrolyte is stirred with a solution of 1.2 molar di-(Z-ethyl-hexyl) phosphoric acid in kerosine, for 40-45 minutes, the ratio of aqueous phase to organic phase being equal to 1:15. There are obtained l. of organic phase containing 19.17 g. indium/l. and 2.4 g. tin/l. The organic phase, into which a part of the lead was carried is washed with an aqueous solution of fiuosilicic acid of the same concentration in the same ratio as in Example 1. There is thereby obtained an aqueous solution containing 45 g. lead/l. which is added to the electrolyte whose indium and tin were extracted, and this mixture is recycled into the electrolysis step.

For the re-extraction of indium, the organic phase is treated with a solution of 9 N HCl, the ratio organic phase to aqueous phase being equal to 11.511, and the contact time being about 10-15 minutes. There are obtained 1.3 l. of an aqueous solution containing 216 g. indium/l. and 0.91 g. tin/l. The organic phase is subsequently treated for re-extraction of tin with a solution of 8 N HCl, the ratio organic phase to aqueous phase being equal to 21:1, and the contact time being of 60 minutes. There are obtained 0.71 liters of an aqueous solution containing 46.5 g. tin/l. and 5.2 g. indium/l.

Example 3 Raw lead containing no indium, but having the usual tin content, is used as starting material. 50 kilograms of raw lead containing 0.2% of tin and traces of indium is electrolytically refined using an electrolyte consisting of 120 g. of fiuosilicic acid per liter and 80 g. lead/1., and applying a current density of 100 a./m. There are obtained 48.5 kg. of refined lead containing less than 0.01% of tin and 30 liters of electrolyte containing 3.2 g. tin/1., 50 g. lead/1., and 116 g. fiuosilicic acid/l.

The electrolyte is admixed with 10 liters of an organic phase containing 1 mole di-(2-ethyl-hexyl) phosphoric acid in kerosine by stirring for about 45-50 minutes in order to extract tin. To remove the extracted lead, the resulting organic phase containing 9.1 g. tin/l. is washed with an aqueous solution of fluosilicic acid, as in the preceding examples.

For the re-extraction of tin, the organic phase is treated with a solution of 8 N HCl, the ratio of organic phase to aqueous phase being equal to 6.7 and the contact time being of 50-60 minutes. 1.5 liters of a solution containing 54.6 g. of tin/l. are obtained. After forming and melting a cement, 82 g. of tin containing 02-03% of indium are obtained.

The process of the invention has been found to have numerous advantages among which are the following improvements.

It permits separation and isolation of indium and tin from the raw lead by using a relatively simple technology with a minimum consumption of both reagents and energy. I

It further results in almost quantitative recovery of indium and tin, both materials being of a maximum purity as recovered.

Finally in the separation of indium and tin, the losses of lead as salts or as residual products are eliminated.

What is claimed is:

1. A process for recoving indium and tin from impure lead which comprises the steps of concentrating the indium and tin in the electrolyte of an electrolytic refining process for lead by recycling said electrolyte to obtain a minimum ratio of lead to tin of 10, liquid-liquid extracting the electrolyte with a solution of di(2-ethylhexyl) phosphoric acid in kerosene, separating the phases, washing the organic phase with an aqueous solution of fiuosilicic acid, re-extracting the indium from the washed organic phase with 9 N I-ICl, re-extracting the tin from the washed organic phase with 8 N HCl, recycling the organic phase to the liquid-liquid extraction step, recycling the electrolyte to the eletcrolytic refining step, and recovering indium and tin from the re-extractions.

2. The process of claim 1 in which the liquid-liquid extraction is carried out with 0.8 to 1.2 molar di(2-ethyl hexyl) phosphoric acid in refined kerosene at a contact time of 30-60 minutes at room temperature, and the ratio of aqueous phase to organic phase is 0.67 to 3.

3. The process of claim 2 in which the re-extraction of indium is carried out with 9 N HCl for 8 to 10 minutes and the re-extraction of tin is carried out with 8 N HCl for 55 to minutes.

4. The process of claim 3 in which the indium and tin are recovered by cementation on aluminum sheet at a pH of 1 to 2 followed by subsequent melting under sodium hydroxide.

References Cited UNITED STATES PATENTS 1,397,222 11/1921 Mathers 204120 1,487,111 3/1924 Linville 204-l20 2,433,770 12/1947 Lebedeff -84 JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner US. Cl. X.R. 204 

